System for reducing fading effects in broadcast receivers



C. L. DAVIS Dec. 5, 1933.

SYSTEM FOR REDUCING FADING EFFECTS IN BROADCAST RECEIVERS Filed March 8, 1930 IN VEN TOR. M 52 9001 ATTORIf/EY Patented Dec. 5,1933

SYSTEM FOR REDUCING FADING EFFECTS IN BROADCAST RECEIVERS Chester L. Davis, Keokuk, Iowa, assignor to Wired Radio, Inc., New York, N. Y., a corporation of Delaware Application March 8, 1930. Serial No. 434,293

Claims. (Cl. 250-20) NT OFFICE My invention relates broadly to radio broadcast receiving systems and more particularly to a circuit arrangement for radio broadcast receivers having means for compensating for fading ef- 5 fects.

One of the objects of my invention is to provide means for automatically compensatingfor the effect of fading upon the operation of a receiving apparatus in radio broadcast reception.

Another-object of my invention is to provide variable resistance means for controlling the biasing potential on the grid circuits of certain of the amplifying'tubes in a receiver according to the amplitude of the incoming" signaling energy for controlling the volume of the reproduced sound. v

A further object of my invention is to provide .a light sensitive cell system which is controllable by the luminosity of a "lamp which is directly controlled in accordance with the received signaling energy for proportionately controlling the biasing potential on certain of the electron tubes jof the receiving apparatus and correspondingly Qcontrolling the amplitude of the reproduced sound.

Other and further objects of my invention residein the circuit arrangement for a radio broadcast receiver as set forth more fully in the specigfication hereinafter following by reference to the accompanying drawing which diagrammatically illustrates the subject matter of my invention.

' The receiver includes the antenna 1 and ground connection 2 in which circuit there is connected the primary winding 3 of the coupling transformer 4. A secondary winding 5 is inductively coupled to the primary winding 3 and connects to the input circuit of the first stage of radio frequency amplification indicated at 6. The output circuit of the amplifier stage 6 is coupled through transformer '7 to the input circuit of thesecondary stage of radio'frequency amplification represented'at 8. A coupling transformer 9 is connected to the output circuit of the electron tube 8 for impressing the signaling energy upon the input circuit of the detector tube 10. The input circuits of the radio frequency amplifier stages 6 and 7 and the input circuit of the detector tube 10 may be tuned by means of the unicontrol condenser system represented at 11.

The output circuit of the detector tube 10 connects through audio frequency transformer 12 with the first stage of audio frequency amplification designated at 14. The output circuit of the audio frequency amplifier 14 is coupled 5.5 through audio frequency transformer 15 with the winding 19 and a multiplicity of secondary Windings, 20, 21, and 22. Secondary Winding 22 supplies alternating current of suitable potential r to the cathode heater circuit 23 which connects to all of the electron tubes in the receiving system. The rectifier tube 24 supplies rectified energy through the filter system 25 to the plate circuits of the several tubes in the receiving apparatus. A potentiometer 26 connects across the output of the filter circuit from which taps 27, 28, 29, and 30 extend'for supplying the required energizing potentials to' the different circuits. The extreme negative end of the potentiometer 26 connects to the grid return circuit of the audio frequency amplifier tubes 14 and 16 through conductor 31. The cathode circuit for the several tubes is common as shown by the conductor 32 and connects to the point 29 on the potentiometer 26 so that the grids of tubes 14 and 16 are supplied with a selected negative potential with respect to the cathode potential. The anode supply potential for the radio frequency amplifier stages 6 and 8 and the detector stage 35 16 is supplied from the positive end of the potentiometer 26 as indicated at 2'7 through the lead 33, the energy passing through audio frequency choke coil 34 and radio frequency choke coil 35. Thelanode supply potential for the audio frequency amplifier stagesl i and 16 is supplied from the positive end of the potentiometer 26 through audio frequency choke coils 36 and 37. The audio frequency choke coils are designed to be responsive to the entire band of audio frequencies which must pass through the output circuit of the final stage of power amplification during the operation'of the sound reproducer 1'7. Theaudio frequency choke coils 36 and 37 are arranged to prevent sudden fluctuations of the power supply in the output system from affecting the sound reproducer 17. The audio frequency choke coil 36 is shunted by a condenser 38 which is in turn shunted by a resistance 39. The choke coil 36 is relatively large as is also the capacity 38 so that the arrangement has a low frequency response. Any variations of current therefor that occur adjacent to the end of the choke coil 36 connected to the positive end of the potentiometer 26 will normally be below audio frequency and dependent on the effect of fading. The resistance 39 has a variable tap 4O thereon by which selected potential may be supplied to the glow discharge tube 41. The glow discharge tube 41 is variable in its luminous properties depending upon the amplitude of the incoming signalin energy. A light sensitive element 42 which may be a selenium cell or a photoelectric cell is mounted immediately adjacent the glow discharge tube 41 so that the conductivity thereof may be changed in accordance with the change in light intensity of the glow discharge tube 41. The light sensitive element or photoelectric cell 42 is shunt connected by variable resistance 43 by which the effective resistance of the light sensitive device may be adjusted. The light sensitive device 42 is connected in series with the grid circuits of the radio frequency amplifier stages through the conductor 44 receiving biasing potential through tap 45 on potentiometer 26.

In the operation of the receiving apparatus of my invention the amplitude of the signaling energy may suddenly increase in the loud speaker 17, increasing the current flow through the choke coils 36 and 3'? and increasing the current flow through resistance 39, thereby increasing the luminosity of glow discharge tube 41. The conductivity of the light sensitive cell path 42 is thereby increased, increasing the energy supply through the grid circuits of the radio frequency amplifier tubes 6 and 8 and controlling the bias potential on the grids of the radio frequency amplifier stages 6 and 8 for reducing the sensitivity of the electron tubes, thereby reducing the amplitude of the signal in the output circuit. When the signal falls below the required level at the sound reproducer 17, the normal sensitivity of the radio frequency amplifier stages 6 and 8 is restored by reason of the decrease in luminous intensity of the luminous discharge tube 41 and the restoration of normal bias on the grid circuits of the electron tube stages 6 and 8. The desired normal bias for required sensitivity of the electron tube system is obtained by adjustment of shunting resistance 43 as well as the adjustment of tap 45 along potentiometer 26. In this manner the receiver may be adjusted for maximum sensitivity for minimum signal amplitude and the control system of my invention functions to prevent rise of the reproduced signaling energy above a predetermined optimum value. The normal energization of the luminous discharge tube 41 is determined by the desired intensity of the reproduced signal emanating from the sound reproducer 17 and when this minimum signal amplitude is determined the adjustment of contact 40 along resistance 39 may be fixed and thereafter requires very little attention.

The choke coil 36 is relatively large in value and is associated with a relatively large condenser 38 so arranged that the glow discharge tube 41 is only operative over a range of current changes within the audio frequency band. That is to say, the large choke coil prevents the normal modulation current effects from reaching the glow discharge tube 41 while abnormal fluctuations of the audio frequency current derived from fading effects will actuate the glow discharge tube 41. The changes in bias energy supplied to the radio frequency amplifier system occur at an audio frequency rate and therefore do not tend to introduce distortion of the signals. Furthermore, the biasing energy is supplied to the tubes which are operated by high frequency signaling energy which is unrectified enabling the signaling intensity to increase or decrease according to the bias potential which is supplied at an audio frequency rate. Due to the arrangement of choke coils 36 and 3'? changes in biasing potential as applied to the radio frequency ampliiier depend wholly upon fading effects in the signaling energy. Hence this biasing potential is unaffected by audio frequency modulation of the signals.

I may adjust the system of my invention to increase the sensitivity of the amplification circuits in the receiver under the effects of fading of the signals. Other changes in the general circuit arrangement of my invention may be made, the fundamental principles to be followed, however, being the control of the biasing potential on the radio frequency amplifier stages according to the amplitude of the signaling energy in the sound reproducer circuit by means of the general arrangement heretofore described.

While I have described my invention in certain preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of 5100 the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows: 1. In a signal receiving system, a multiplicity of electron tubes coupled for successively acting 195 upon received signaling energy, power supply circuits for said electron tubes, a series circuit connected with the output of one of said electron tubes, said series circuit including an impedance element, a condenser connected in'shunt with in shunt with said condenser, and a luminous discharge device connected in shunt with a portion of said resistance, a light sensitive cell aligned with said luminous discharge device, said light sensitive cell being disposed in series with said source of potential and the input circuit of a preceding electron tube for controlling the operating characteristics of the preceding elec- .116 said impedance element, a resistance connected tron tube in accordance with the amplitude of 12 0 the signaling energy in the output circuit of the aforementioned electron tube and proportional to the luminosity of said luminous discharge device.

2. In a signal receiving system, a multiplicity .125

of electron tubes each having input and output circuits, means coupling'the input and output circuits of said electron tubes whereby said electron tubes are successively operated by-incoming signaling energy, a series connected path in the ,130

output circuit of one of said electron tubes, power supply means for the circuits of said electron tubes, an impedance element connected in said series circuit, a tuning device connected across said impedance element, a potentiometer in shunt .135

with said impedance element, a glow discharge tube connected across said potentiometer, a light sensitive cell, a series circuit includingsaid source of potential, said light sensitive cell and theinput of a preceding electron tube, said light sensitive cell being directly disposed to variations in light intensity of said luminous discharge tube for controlling by the operation thereof the operating characteristics of the said preceding electron tube.

3. In a signal receiving system, a .multiplicity of electron tubes each having input andoutput circuits, means coupling the output circuit of one electron tube with the input circuit of asucceeding electron tube, power supply means and cir-,1 5

cuits including choke coils for energizing said electron tubes, a series circuit connected with the output circuit of one of said electron tubes, said series circuit includinga condenser connected in shunt with one of said choke coils, a resistance connected across said condenser, a glow discharge tube connected across a portion of said resistance, a light sensitive cell exposed to light from said glow discharge tube, and a series path including said light sensitive cell and power supply means, and the input circuit of a preceding electron tube.- V

4. In a device of the class described, a plurality of electron tube stages of radio frequency and audio frequency amplification and an electron tube detector, power supply means and power filtering means for supplying constant current to the input and output circuits of said electron tube stages, a luminous device connected in shunt with a portion of said filtering means and responsive to variations in current flow through the output circuits of said audio frequency stages and a photoelectric device under the influence of variations in the intensity of light emanating from said luminous device and connected with the input circuits of said radio frequency stages for controlling the grid bias potential applied thereto so as to compensate for variations in the intensity of the received signals.

5. In a radio receiving system, radio frequency amplification means including electron tubes, audio frequency amplification means including electron tubes, an electron tube detector interconnecting the last stage of radio frequency amplification and the first stage of audio frequency amplification, a source of constant current, a filtering device therefor and connections between said source of constant current and the input and output circuits of the electron tubes in said receivingsystem, means including a luminous discharge device in shunt with a portion of said filtering device for emitting light the intensity of which varies in accordance with variations in the potential drop through said portion of the filtering device, due to variations in the amplitude level of the received audio frequency signals, and means including a photoelectric device responsive to variations of intensity of the light emitted by said luminous device for controlling the bias potential applied to the grids of the electron tubes in said radio frequency amplifier whereby the amplitude level of the received audio frequency signals may be maintained substantially independent of fading eifects.

CHESTER L'. DAVIS. 

